1. Field of the Invention
The present invention relates to a charged particle beam exposure method and a charged particle beam exposure device, and more particularly, to a method for creating exposure data for exposing patterns on a semiconductor wafer by means of a charged particle beam, such as an electron beam exposure, and a charged particle beam exposure device for implementing this method.
2. Description of the Related Art
The a charged particle beam exposure, such as an electron beam, is able to expose patterns of the sub-micron order and is used in the fabrication of highly integrated LSIs. In particular, recently, in addition to its use in forming masks, methods whereby the charged particle beam is irradiated directly onto the resist formed on a semiconductor wafer have been used.
In the design stage for LSIs, pattern data for a multi-layered structure is created in order to form a desired integrated circuit. The resist on a semiconductor wafer or the resist on a mask substrate is exposed according to this pattern data. The resist is subject to a chemical reaction generated by the energy of a charged particle beam which is irradiated onto the resist layer.
In this case, it is important to take note of the proximity exposure effect, which is caused by forward or backward scattering of the beam in the resist when the charged particle beam is irradiated onto the resist. The proximity exposure effect is a phenomenon which causes the energy of a charged particle beam irradiated onto a particular region to spread into adjacent regions due to scattering of the beam. For example, in a region where the exposure pattern density is high, after developing, a pattern may have broadened due to the effect of beam energy from a charged particle beam irradiated onto an adjacent exposure pattern region.
Alternatively, in a region where the exposure pattern density is low, there will be no effect due to energy from adjacent regions, and the pattern after developing may be condensed or narrow.
Therefore, the designed exposure data must be corrected, taking this proximity exposure effect into consideration. The present applicants have proposed such a method for correcting exposure data in Japanese Patent Application 8-13354 (Japanese Unexamined Patent 8-321462), dated Jan. 29, 1996.
Briefly stated, in the method proposed in this patent application, a plurality of mask areas are generated in a sub-field, the pattern density in each of these areas is corrected in accordance with the effects due to the pattern density in surrounding areas, an effective pattern density taking the proximity exposure effect into account is determined, the quantities of exposure (which means beam intensity exposure time, herein after quantity of exposure) for the patterns in each area are revised in accordance with this effective pattern density, and supplementary exposure patterns are generated additionally.
However, since the supplementary exposure patterns are produced by generating areas of a particular size without relation to the position of patterns located in a sub-field, and by taking these areas as the pattern units, there are cases where it is not possible to generate a suitable supplementary exposure pattern corresponding to an actual exposure pattern. Moreover, if the pattern density in an area is corrected with regard to the effect of the pattern density in surrounding areas, in some cases, the distance between the areas may be different from the distance between the actual pattern groupings, and in this event, it is not possible to account for the proximity exposure effect accurately. Furthermore, if the aforementioned areas are generated, the pattern density is corrected, and a supplementary exposure pattern is produced, separately in a similar manner, for each of a plurality of sub-fields which have the same exposure pattern and are positioned by repetition of, then this lengthens the data processing step for no purpose, and is not suitable for creating exposure data for highly integrated LSIs.
Furthermore, when using charged particle beam exposure, the throughput in variable square beam exposure systems deteriorates as the number of patterns increases, and therefore exposure by means of a block mask which is broader than the variable rectangle and comprises a plurality of patterns is used for regions wherein the same pattern is formed repeatedly. Since a relatively broad region comprising a plurality of patterns can be exposed in a single beam irradiation cycle, throughput can be increased.
If a block mask is used, then a plurality of patterns are comprised within a block mask and there may be respective differences between the line widths in these patterns. However, in block mask exposure, all of the patterns contained therein must be exposed with the same quantity of beam. According to the method for generating exposure data described above, the quantity of exposure is set depending on the pattern shape. In particular, the quantity of exposure is reduced when the line width is thick, and it is increased when the developed line width is narrow. This is because, when the line width is thick, the actual quantity of exposure is increased due to the proximity exposure effect from surrounding regions, and the developed line width becomes thicker, whereas when the line width is narrow, the developed one becomes narrower. Accordingly, when a block mask is used, the minimum line width is detected, for example, and the quantity of exposure is set according to this line width.
In this case, if there is a pattern with a narrow line width in a portion of the block mask, there may be cases where the quantity of exposure is set to an excessively high value accordingly, and the pattern width after developing will become too thick.
A problem arising when using block masks is that since there is a high pattern density in the block mask, when beam exposure is conducted repeatedly using a block mask, there is a tendency for the developed patterns to become thicker, due to the effect of xe2x80x9cCoulomb interactionxe2x80x9d. This effect is especially notable at the peripheral edges of regions which are exposed repeatedly using a block mask.
Therefore, it is an object of the present invention to resolve the aforementioned problems of the prior art by providing a charged particle beam exposure method and a charged particle beam exposure device for implementing same, whereby it is possible to create exposure data enabling patterns of greater accuracy to be formed.
It is a further object of the present invention to provide a charged particle beam exposure method and a charged particle beam exposure device for implementing same, whereby it is possible to create exposure data which resolves inadequacies due to divergence between areas which are generated uniformly within a sub-field and the actual exposure patterns.
It is a further object of the present invention to provide a charged particle beam exposure method and charged particle beam exposure device for implementing same, whereby it is possible to take account of the effects of the pattern densities in surrounding areas, with respect to the positions of the actual patterns.
It is a further object of the present invention to provide a charged particle beam exposure method, whereby a suitable quantity of exposure is set for charged particle beam exposure using a block mask.
It is a further object of the present invention to provide a charged particle beam exposure method, whereby the effects of Coulomb interaction are eliminated and pattern variations due to the proximity exposure effect are also eliminated, in charged particle beam exposure using a block mask.
In order to achieve the aforementioned objects, in a charged particle beam exposure method, wherein exposure data comprising exposure pattern data for each of a plurality of sub-fields located in a main field is determined from pattern data comprising pattern data for each of the sub-fields, and a material is exposed in accordance with the exposure data, the basis of the present invention is a charged particle beam exposure method comprising the steps of: (a) generating a plurality of areas within the sub-fields; (b) determining the pattern density within each of the areas, and correcting the pattern density in accordance with the pattern density of areas surrounding the area and the distance between areas; (c) generating a supplementary exposure pattern in the area when the corrected pattern density for the area is lower than a prescribed reference exposure density; and (d) exposing the material in accordance with exposure data comprising the supplementary exposure pattern data appended to the pattern data.
A first invention comprises a step for further generating a supplementary exposure pattern in areas lying between pattern existing regions where the patterns are located, and having a pattern density higher than the reference exposure density, when the distance between the pattern existing regions is greater than a prescribed reference distance.
According to the first invention, even if there is mismatching between an exposure pattern and an area generated in a sub-field, and no supplementary exposure pattern is produced when it is judged simply by the pattern density in the area, it is still possible to generate a supplementary exposure pattern when the distance between the pattern existing regions is greater than a set distance. Therefore, a suitable supplementary exposure pattern can be generated, providing an appropriate proximity exposure effect, even when there is mismatching between the exposure pattern and the area.
In a second invention, the supplementary exposure pattern has a desired exposure energy distribution according to the resist material formed on the material.
According to the second invention, even if the spreading characteristics of the exposure beam energy vary depending on the resist material, it is possible to generate a supplementary exposure pattern having an exposure energy distribution corresponding to these characteristics. Therefore, a suitable proximity exposure effect can be achieved in accordance with the resist material used.
In a third invention, the step (a) generates a plurality of areas in point symmetry from the center of pattern existing regions in the sub-field, within a peripheral region of a prescribed range.
According to the third invention, mismatching between exposure patterns and areas is prevented by generating the areas in point symmetry from the center of pattern existing regions, and therefore supplementary exposure patterns which are matched to the exposure patterns can be generated.
In a fourth invention, the step (b) determines the pattern density within each of the areas, and corrects the pattern density in accordance with the pattern density of areas surrounding the area, and the distance between pattern existing regions in the areas.
According to the fourth invention, since the effect of exposure energy from patterns in surrounding areas is determined by the distance between pattern existing regions, the effect of this exposure energy can be determined more accurately. Consequently, a more accurate supplementary exposure pattern can be generated. Desirably, the distance between pattern existing regions is taken as the distance between the centers of gravity of the pattern existing regions. In a fifth invention, when a plurality of sub-fields comprising the same pattern data are positioned by repetition, the steps (a)-(c) are implemented for the first of the repeated sub-fields, and if no supplementary exposure pattern is generated in the first sub-field, the steps (a)-(c) are omitted for the remaining sub-fields, with the exception of at least a portion thereof.
According to the fifth invention, the speed of calculation for repeated sub-fields can be shortened.
In order to achieve the aforementioned objects, in a sixth invention, the quantity of exposure set for a block mask is not set as the quantity of exposure corresponding to the minimum line width of the block exposure pattern data, but rather, if there exists block exposure pattern data which is narrower than a previously determined proposed minimum line width, then it is set as the quantity of exposure corresponding to this proposed minimum line width for the blockmask. Therefore, even if there exists block exposure pattern data which is narrower than the design rules, it is possible to avoid setting an excessively high quantity of exposure.
In other words, in a charged particle beam exposure method, wherein a charged particle beam passing through a block mask containing a plurality of patterns is irradiated onto a material to be exposed, the present invention comprises the steps of: specifying a proposed minimum line width for pattern data in the block mask; setting a quantity of exposure corresponding to the proposed minimum line width as the quantity of exposure for the block mask, when the minimum line width of the pattern data in the block mask is narrower than the proposed minimum line width, and setting a quantity of exposure corresponding to the minimum line width of the pattern data as the quantity of exposure for the block mask, when the minimum line width of the pattern data in the block mask is thicker than the proposed minimum line width; and irradiating a charged particle beam having the set quantity of exposure onto the material to be exposed by passing it through the block mask.
In the aforementioned invention, in the step of specifying the proposed minimum line width, a plurality of the proposed minimum line widths are set in a prescribed order of priority, and a quantity of exposure corresponding to the proposed minimum line width which is close, of the set plurality of proposed minimum line widths, to the minimum line width of the pattern data in the block mask, is set as the quantity of exposure for the block mask.
Furthermore, in a charged particle beam exposure method wherein a charged particle beam is shaped in accordance with variable rectangular pattern data and is irradiated onto a material to be exposed, the present invention comprises the steps of: specifying a proposed minimum line width corresponding to the variable rectangular pattern data; setting a quantity of exposure corresponding to the proposed minimum line width as the quantity of exposure for the variable rectangular pattern, when the minimum line width of the variable rectangular pattern data is narrower than the proposed minimum line width, and setting a quantity of exposure corresponding to the minimum line width of the variable rectangular pattern as the quantity of exposure light for the variable rectangular pattern, when the minimum line width of the variable rectangular pattern data is thicker than the proposed minimum line width; and shaping a charged particle beam having the set quantity of exposure irradiating into the variable rectangular beam and shining the beam onto the material to be exposed.
By setting the aforementioned proposed minimum line widths, the quantity of exposure is prevented from becoming excessively high, in the case of variable rectangular pattern data, also.
Furthermore, in a charged particle beam exposure method wherein a charged particle beam passing through a block mask containing a plurality of patterns is irradiated repeatedly in a matrix fashion onto a material to be exposed,
the present invention comprises the steps of:
exposing block exposure patterns corresponding to regions located at the perimeter of the matrix in the matrix-shaped exposure region, by means of a variable rectangular beam; and
exposing block exposure patterns corresponding to regions located at the center of the matrix in the matrix-shaped exposure region, by means of a charged particle beam passing through the block mask.
According to this invention, when conducting exposure by block mask repeatedly in a matrix fashion, by exposing regions at the perimeter of the matrix with the patterns contained in the block mask by means of respective variable rectangular beams, rather than using exposure by block mask, the effect of Coulomb interaction is prevented and it is possible to avoid thickening of line patterns in perimeter regions.
Moreover, in a charged particle beam exposure method wherein exposure data comprising exposure pattern data for each of a plurality of sub-fields existing in a main field is determined from pattern data comprising pattern data for each of the sub-fields, and a material is exposed in accordance with the exposure data, the present invention comprises the steps of: generating a plurality of areas within the sub-fields; determining the pattern density within each of the areas, and correcting the pattern density in accordance with the pattern density of areas surrounding the area, and the distance between areas; generating a supplementary exposure pattern in the area when the corrected pattern density for the area is lower than a prescribed reference exposure density; and exposing the material in accordance with exposure data comprising the supplementary exposure pattern data appended to the pattern data; wherein the reference exposure density is lower for areas having a block mask pattern containing transmission holes in a lattice configuration, than for other areas.
According to the aforementioned invention, it is possible to set the reference exposure ratio, which is the reference for generating supplementary exposure pattern data, to a low figure, when a block mask is used which contains cross-lines in the block exposure pattern in order to prevent Coulomb interaction effects, and hence the generation of unnecessary supplementary exposure pattern data can be prevented.